Reactors for petroleum refining can remain viable from a structural standpoint for multiple decades. However, during this lengthy time period, advancements in refining technology may lead to improved designs or methods that do not match the original reactor structure. Systems and/or methods that allow older reactors to be upgraded to take advantage of newer technologies can result in substantial cost savings, in comparison with retiring a reactor and building a new structure.
Many conventional or heritage catalytic reactors for petroleum refining are single bed reactors. Some of these reactors can have long reactor beds relative to the inner diameter of the reactor. For example, a ratio of the length of the reactor bed to the inner diameter of the reactor can be at least about 4 to 1 or greater. Although the long reactor bed can hold a large volume of catalyst, the single bed configuration can lead to reduced catalyst effectiveness.
One reason for reduced catalyst effectiveness can be poor flow distribution. A poor flow distribution can develop within a catalyst bed for a variety of reasons. The length of the catalyst bed can be one factor, with longer beds typically having an increased likelihood of flow distribution problems. Another problem can be having a low liquid mass flux through the bed, where the amount of liquid flowing through the bed per unit area and per unit time is too low to provide good flow characteristics. Other factors that can contribute to a poor flow distribution can be related to flow bridging within the bed, poor loading of catalyst into the catalyst bed, or liquid plugging. An example of a poor flow distribution can be “channeling” of a feed, where the feed preferentially passes through a portion of the catalyst while exposing other portions of the catalyst to little or no fluid flow. In a single bed reactor, if a problem develops with the flow pattern of the fluids passing through the single catalyst bed, the resulting poor flow distribution will likely continue for the entire length of the bed.